Foam depth reaching 2 feet above slats in a swine finishing facility
Foam depth reaching 2 feet above slats in a swine finishing facility

Foaming on the manure surface in deep-pit swine barns is not a new phenomenon, but until recently, spontaneous foaming was rare. Foaming incidence has increased significantly since 2008, and concerns over the potential hazards posed by foam have risen accordingly.

Typically, several inches of foam can build up and cover the surface in deep-pit swine finishing barns, but foam depths of 5 feet or more have been observed. Foam traps and holds biogases emitted during anaerobic decomposition of stored manure. Disrupting the manure or foam surface releases bursts of biogas with methane concentrations of 50 percent to 70 percent by volume. When mixed with ambient air, the resulting concentration can be in the explosive range (5 percent to 20 percent). This increases the potential for flammable gas levels when a heater, motor or light switch is activated or when a worker begins spark-inducing maintenance tasks, such as grinding or welding.

Foaming incidents  seem to be confined to Minnesota, Illinois and Iowa, with sporadic cases outside the upper Midwest. Foaming manure has been implicated as the underlying cause of several barn explosions (flash fires) in those three states.

Recent fires associated with foaming manure have caused extensive building damage. Pigs were severely burned and most had to be immediately sent to market or euthanized. No human deaths have been associated with the fires, but workers were injured after being propelled by the blast or exposed to intense heat. Two workers were hospitalized with second- and third-degree burns.

Preliminary Findings 

In early 2010, a preliminary study investigated foaming causes and the link between foaming and barn explosions. The research included a small-scale qualitative survey of Midwestern pork producers, conversations and field visits.

Approximately 25 percent of the survey respondents reported some barn foaming, with about half of those barns having levels deeper than 6 inches. No commonality was found in the incidence of foaming and/or flash fires with building type or age, feeder or waterer style, manure characteristics, pit additives, feed waste, swine genetics, diet or management.

Most fires or explosions have occurred when barns were empty in cooler weather. In those cases, ventilation fans were off or were running at minimal speeds. Many producers reported flash fires on the surface of the manure pit (without foam) between pig groups when welding was being done inside barns. At least three of the larger explosions occurred in barns that did not have foam, but the manure in the pits was being agitated with minimal ventilation.

Microbial Connections

Foaming also has been seen in wastewater treatment facilities, which led researchers to hypothesize that filamentous/actinomycete bacteria species might be the cause of manure foaming in swine facilities. When microbes taken from pits were screened to identify microbial community differences, DNA fingerprints showed similarities in microbial diversity between the top and bottom layers of foaming manure samples, and clear differences were observed between foaming and non-foaming samples, indicating potential differences in bacterial populations.

Additional DNA testing showed significant differences between foaming and non-foaming samples. Actinomycetaceae, Alcaligenaceae, Bacillaceae, Bacillales incertae sedis and Enterococcaceae bacteria were present in significantly higher percentages in foaming samples.

A gene probe can be designed to target specific filamentous bacteria species, but results show manure foaming was not related to the amount of the filamentous bacteria in manure taken from buildings with foaming pits.

Adding Monensin to Pits 

In late 2011, a research study involved sites with typical grow/finish buildings (1,000- to 1,100-head, single- or double-wide, 8-foot-deep pits). Sites were chosen with groups of four barns to ensure similar management style, genetics, diet and building age at each test site. The four barns on each site were randomly assigned to dosing treatments of 0 (control), 2.5, 5, and 10 pounds of Rumensin 90 (monensin) per 100,000 gallons of manure.  (See accompanying table.)

As of August 2012, based on our findings, we are recommending that producers who have pits at risk for foaming add Rumensin 90 at a rate of 5 pounds per 100,000 gallons. A lower rate may help reduce foaming, especially if additional Rumensin can be added at a later date or more time can be allowed before assessing results. While this is our current advice, more work is needed to determine the best dosing rate, timing or season of application, as well as duration of effects (several months are expected). About two weeks is needed after treatment to see a reduction in foaming. Take care not overdose the pit, which results in a “dead” pit with no biological activity.

Here are the preferred methods to use Rumensin to control manure foaming (listed in order of preference):

1. In an all-in/all-out system after the pigs are marketed, sprinkle Rumensin 90 evenly throughout the empty room or building. As the empty building is power-washed, the additive will be  worked through the slats, falling onto the manure surface.

2. If the room is occupied, carefully drop Rumensin 90 through the slat openings. The more evenly the product is applied around the room, the faster and better it will work. This can be accomplished by using a small PVC pipe and funnel (or using a small cup or tablespoon). This method works well under watering cups/bowls or nipple waterers, helping the product move into the pit.

3. Add Rumensin90 through manure pump-out ports. With this method, it takes time for the product to diffuse throughout the manure pit, which may delay or not accomplish the intended goal. Agitation may help work the product into manure, but be sure to avoid releasing gases (methane and hydrogen sulfide) and know that agitation may make foaming worse in the short-term.

Be sure to avoid human or pig exposure to Rumensin90, which causes burning eyes, skin reactions and lung irritations if inhaled or ingested.

 

Testing the Monensin Theory

The following table contains the foam depth (inches) at the time Rumensin 90 was added to the pits, along with foam depths three and six weeks later for the four application rates. Each column is a single pit within a site.

 

 

Site 1

Site 2

Site 3

Application

   rate, pounds per 100,000 gallons

 

0

 

2.5

 

5

 

10

 

0

 

2.5

 

5

 

10

 

0

 

2.5

 

5

 

10

 

 

 

 

 

Foam depth, inches

 

 

 

 

Pre-application

 

20

20

20

20

21

18

21

18

11

14

6

20

3 weeks post

   application

10

0

0

0

12

17

13

12

14

10

1

16

6 weeks post

   application

0

0

0

0

6

0

0

0

14

9

0

3

Source: University of Minnesota

Testing poloxalene (Bloat Guard) at other sites was not successful in reducing foam.

Note that Rumensin 90 is not environmentally approved to be added to manure in a pit if the nutrients will be applied to land. Always check with your state pollution-control agency for requirements and regulations.

Editor’s note: Survey, laboratory and field research was funded by the Minnesota Agricultural Experiment Station Rapid Agricultural Response Fund and Minnesota Pork Board. Other University of Minnesota researchers on the team included Neslihan Akdeniz Onuki; Brian Hetchler, PE; Bo Hu; David Schmidt, PE; from the bioproducts and biosystems engineering department; from the animal science department, Lee Johnston and Jerry Shurson.